Rashi on Exodus 21:3/רש"י על שמות כ״א:ג׳

1אם בגפו יבא IF HE CAME IN BY HIMSELF — This means that he was unmarried — as the Targum renders it אם בלחודוהי, if he came in “alone”. The term בגפו is the same as גף) בכנפו being synonymous with כנף wing, skirt) i. e. he came in only just as he was, alone, merely wrapped in his garment: so that בגפו, “in his skirt”, means “in the skirt of his garment”.

2בגפו יצא HE SHALL GO OUT BY HIMSELF — This intimates that if he was unmarried originally (when he came in), his master is not allowed to give him against his will a Canaanitish handmaid with the object of raising slaves (Kiddushin 20a).

3אם בעל אשה הוא IF HE BE MARRIED to an Israelite woman (Mekhilta),

4ויצאה אשתו עמו then HIS WIFE SHALL GO OUT WITH HIM — But who brought her in (into the state of service) that the text has to state she shall go out? But by saying this Scripture intimates that he who acquires a Hebrew servant is bound to provide his wife and children also with food (Mekhilta; Kiddushin 22a).